In high-rise buildings of up to about 197 ft, i.e., approx. 60 m, that is, with about 15-20 floors, the stairwell can reliably be kept free from smoke by a relatively homogeneous overpressure if, for example, supply air is blown in at the lowermost area of the stairwell and, simultaneously, via the air supply shaft through the inlet openings into the stairwell. This technique is the prior art on which the invention is based.
When buildings become higher, it becomes substantially more difficult, however, to establish a relatively homogeneous pressure column over the entire height of the stairwell. The reason for this lies in the geometry of the stairwell. The windings of the stairs and the banisters, but also large parts of the stairwell, form flow resistances. This leads to an average of 0.04 lb/ft2, which is 2 Pa (Pascal) pressure being lost per floor.
According to the European Standard EN 12101, Part 6, Issue September 2005, the following is prescribed for smoke-free evacuation paths in buildings:                Door opening force maximally 100 N (which is 22.5 lbf),        Overpressure in the stairwell with closed doors relative to the floors 50 Pa±10% (which is 1.04 lb/ft2), and        mean airspeed in the opened entrance door between the stairwell and the utilization unit≧2 m/s (≧6.56 ft/s) in the case of a fire-fighting operation by the fire department.        
As the admissible pressure range is thus between 0.94 and 1.15 lb/ft2, i.e., 45 and 55 Pa, only five of the 15-20 floors are pressurized correctly in the above example. All floors above that have a pressure lower than 0.94 lb/ft2, i.e., lower than 45 Pa.
According to the prior art, this problem can be addressed by providing the inlet openings already mentioned from about the ninth floor; they are provided, for example, at every third floor. Through them, air is let into the stairwell from the air supply shaft, which is usually adjacent to the stairwell. A stable homogeneity of the pressure can thus be obtained over the entire height of the building.
However, this only applies to buildings up to a certain height. Given the efforts for increasingly higher high-rise buildings, for example beyond 393 ft, i.e., 120 m, physical effects such as the stack effect cannot remain left aside. In particular, the stack effect caused by the temperature difference between the internal and the external temperature (for example in the summer and in the winter) has negative effects on the forces for opening a door, and does so already during normal operation of the building, not just in extreme cases.
The following table shows a sample calculation for a high-rise building with 42 floors; the table shows how the pressures between the stairwell and the utilization unit adjust in normal operation, during the summer and the winter. As a rule, in the case of pressures higher than 1.04 lb/ft2, i.e., 50 Pa, it is difficult, if not impossible, for a person of normal weight and strength to open a door. The above-mentioned door opening force according to EN 12101-6, which is limited to a maximum of 22.5 lbf, i.e., 100 N, is exceeded.
In the table, the following notation is used for designating floors: floor 0 is the ground floor. Floor 1 is the first floor above the ground floor. Floor n in the n-th floor above floor 0. This system is different from the notation commonly used in the USA where floor 1 stands for the ground floor.
TABLE 1Overpressures of the stairwells relative to the floors in an emergency and in normalventilation operation while maintaining a minimum overpressure of 10 Pa anddifferent temperature conditionsHeightTemperatures theTemperaturesTemperatures higherabovesame on the insidehigher on the insideon the outsideseaand outsidethan the outsidethan the insidelevelΔpemerg-op.Δpnormal-op.Δpemerg-op.Δpnormal-op.Δpemerg-op.Δpnormal-op.FloormPaPaPaPaPaPa 0.0.0094.810.710.010.0149.965.8(Ground)Floor 1. Floor4.46592.410.713.916.3145.864.0 2. Floor8.9389.910.617.822.7141.662.3 3. Floor12.3088.110.620.827.4138.561.0 4. Floor15.6786.310.623.732.2135.359.7 5. Floor19.0484.410.626.737.0132.258.4 6. Floor22.4182.610.629.641.8129.157.1 7. Floor25.7880.710.632.646.5125.955.8 8. Floor29.1578.910.535.551.3122.854.5 9. Floor32.5277.010.538.556.1119.753.110. Floor35.8975.210.541.460.9116.551.811. Floor39.2673.410.544.365.6113.450.512. Floor42.6371.510.547.370.4110.349.213. Floor46.0069.710550.275.2107.147.914. Floor49.3767.810.553.280.0104.046.615. Floor52.7466.010.456.184.7100.945.316. Floor56.1164.110.459.189.597.744.017. Floor59.4862.310.462.094.394.642.718. Floor62.8560.510.465.099.191.441.419. Floor66.2258.610.467.9103.888.340.120. Floor69.5956.810.470.9108.685.238.821. Floor72.9654.910.373.8113.482.037.522. Floor76.3353.110.376.8118.278.936.123. Floor79.7051.210.379.7122.975.834.824. Floor83.0749.410.382.7127.772.633.525. Floor86.4447.610.385.6132.569.532.226. Floor89.8145.710.388.6137.366.430.927. Floor93.1843.910.291.5142.063.229.628. Floor96.5542.010.294.5146.860.128.329. Floor99.9240.210.297.4151.657.027.030. Floor103.2938.310.2100.4156.453.825.731. Floor106.6636.510.2103.3161.150.724.432. Floor110.0334.710.2106.3165.947.623.133. Floor113.4032.810.1109.2170.744.421.834. Floor116.7731.010.1112.2175.541.320.535. Floor120.1429.110.1115.1180.238.219.236. Floor123.5127.310.1118.1185.035.017.837. Floor126.8825.410.1121.0189.831.916.538. Floor130.2523.610.1124.0194.628.815.239. Floor133.6221.810.0126.9199.325.613.940. Floor136.9919.910.0129.9204.122.512.641. Floor140.3618.110.0132.8208.919.411.342. Floor143.7316.210.0135.8213.716.210.01 Pa is approximately 0.021 lb/ft2 and 1 m is approximately 3.28 ft.